How to change the default namespace for issuing the kubernetes command?

In previous article, we have created POD and service.

After hearing too much about the kuberenetes, I thought of start learning about it. Being from the openstack background, I initially planned to use openstack for learning the kubernetes but then I decided to use minikube on MAC with virtual box provider for my initial learning and then gradually moving to use kubernetes on cloud platform like openstack. Starting the kubernetes using minikube is really a cake-walk. Once it’s initialized, usually people are tempted to start the first pod or deployment, I was too but before doing that I thought of checking what is present in minikube by default. In this article, I am going to shed some light on the default resources of minikube.

In minikube openssl command is not available by default and it’s not possible to install the package using package manager then how can we generate the SSL certificate for user communication. By default minikube user is using the certificats.

In this article, I will be sharing some useful ES tips. I will be keep on adding the tips to this article over the peroid of time.

In the previous articles, we have seen the ELK setup using docker container. I wanted to try the elasticsearch using clustered based setup but I was facing some issues while running the elasticsearch in clustered mode hence I started exploring other options. Finally I decided to run the ES as a process on MAC but point of worry for me whether it will allow me to run the multiple ES processes on a single machine since each process of ES will try to use the port 9200 but then I read the official doc and found that default port range for ES is 9200-9300 this means it will be using any available port from this range hence if 9200 is already used by one process of ES then second will use next one which could be 9201.

After deploying the multinode ES setup, I thought of issuing the various apis to see the results. I am categorizing this article as cheat sheet for ES.

In the previous article, we have started the docker containers using docker run command, and while starting the ES container we haven’t used the persistent storage to save the indexes which means that if container is stop/start then all data will be lost. If you don’t trust me perform the stop/start of container and you will see that indices are missing.

I recently started learning the ELK stack. Best source of information which I found is the official documentation provided by Elasticsearch.co While reading the ELK I found the new component.. okay not new but which is relatively new to existing ELK stack is beats. I covered beat also in my study notes. In this series I will be providing the setup information and various other hacks related to ELK.

In this article I am going to share some tips about accessing the service from external world. In previous articles, I have talked about accessing the service from client and host machine, explaining the network traffic workflow. While creating a service you can decide whether service should use routing mesh, host mode or external load balancer to access the service.

Route mode mesh

Created the service using following command. As we haven’t specified any mode while creating the service hence by-default it’s using routing mesh. As soon as I have created the service two containers (tasks) are spawned on worker1 and worker2 nodes.

docker@manager1:~$ docker service create --name my-web --publish published=8080,target=80 --replicas 2 nginx

docker@manager1:~$ docker service ls
ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
2spnybgkb7pk        my-web              replicated          2/2                 nginx:latest        *:8080->80/tcp

docker@manager1:~$ docker service ps my-web
ID                  NAME                IMAGE               NODE                DESIRED STATE       CURRENT STATE           ERROR               PORTS
dz17mt27dsjx        my-web.1            nginx:latest        worker1             Running             Running 5 minutes ago
xr2p01g7da2x        my-web.2            nginx:latest        worker2             Running             Running 5 minutes ago

Even though these containers are running on worker1 and worker2 only when manager nodes are not acting like worker nodes still I am able to access the service using the IP address of manager1 on port 8080. Same is applicable for all manager nodes present in cluster.

docker@manager1:~$ sudo iptables -t nat -L | grep 8080
DNAT       tcp  --  anywhere             anywhere             tcp dpt:webcache to:172.18.0.2:8080
docker@manager1:~$

If the service is already created, existing service can be updated to publish the port.

Host mode

As we have seen in case of Host routing mode mesh ports are getting published on all nodes present in swarm cluster. But if you want to publish the ports only on those nodes on which container is running then instead of using no mode option you should have specified mode=host option while creating the service. Also, global mode is used which indicates that this service should get started on all the worker nodes present in swarm cluster.

root@manager2:~# docker service create --name my-web --publish published=8080,target=80,mode=host --mode global nginx

root@manager2:~# docker service ls
ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
m0k3ivut1453        my-web              global              2/2                 nginx:latest

root@manager2:~# docker service ps my-web
ID                  NAME                               IMAGE               NODE                DESIRED STATE       CURRENT STATE           ERROR               PORTS
zj2wreoo2ydz        my-web.j1g6ylbezhhq6d6qwri85vkgq   nginx:latest        worker1             Running             Running 2 minutes ago                       *:8080->80/tcp
vzjt5m2zz7eo        my-web.egy0qr3u15qr8p26p3wpt6ctr   nginx:latest        worker2             Running             Running 2 minutes ago                       *:8080->80/tcp

Question may arise what’s the purpose of using global option in the service creation part, as we are specifying the published and target port 53, if we are having 2 worker nodes and we are going to create service using replication mode with scale of 4, it will try to start 2 containers on each node, it may lead to conflict on port usage. To avoid this scenario, two approaches are available:

1) Skip the target port option so that swarm can chose random port for each tasks 2) Use the global mode which will help to start the container equal to the number of worker nodes avoiding the conflicting situation.

Changing access mode of service from VIP (Virtual IP) to dnsrr (DNS round robin).

root@manager2:~# docker service ls
ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
wnor2cjt0rru        my-web              global              2/2                 nginx:latest

root@manager2:~# docker service ps my-web
ID                  NAME                               IMAGE               NODE                DESIRED STATE       CURRENT STATE            ERROR               PORTS
8zlu8wlhw1f7        my-web.j1g6ylbezhhq6d6qwri85vkgq   nginx:latest        worker1             Running             Running 48 seconds ago                       *:8080->80/tcp
xyajqefq32ml        my-web.egy0qr3u15qr8p26p3wpt6ctr   nginx:latest        worker2             Running             Running 48 seconds ago                       *:8080->80/tcp

root@manager2:~# docker service inspect my-web --pretty

ID:             wnor2cjt0rru3y91bdukvwj3y
Name:           my-web
Service Mode:   Global
Placement:
UpdateConfig:
 Parallelism:   1
 On failure:    pause
 Monitoring Period: 5s
 Max failure ratio: 0
 Update order:      stop-first
RollbackConfig:
 Parallelism:   1
 On failure:    pause
 Monitoring Period: 5s
 Max failure ratio: 0
 Rollback order:    stop-first
ContainerSpec:
 Image:         nginx:latest@sha256:cf8d5726fc897486a4f628d3b93483e3f391a76ea4897de0500ef1f9abcd69a1
Resources:
Endpoint Mode:  dnsrr
Ports:
 PublishedPort = 8080
  Protocol = tcp
  TargetPort = 80
  PublishMode = host